07 toyota 4runner system upgrade options

i hope someone on here has experience with the 03-08 4runners. i have an 07 and just installed a pioneer AVIC-F90BT double din nav/dvd unit. in my previous vehicle i had installed a memphis 2-channel amp bridged to a 12 inch sealed box. although the sound was good, it was a little too much for my use. i also had an older nakamichi 2-channel amp for the fronts. the nakamichi sounded awsome, no distortion at high volume levels. anyways, i want to upgrade my 07 4runner but would like some quality sound, so im thinking of going the nakamichi route again for the amp. the older amps are small and can be hidden well. i really dont want to mount it on the back of the rear seat and it wont fit under the front seats because of the vents. anyone place them in the side panels in the back cargo area? id love to see pics if you have. the front speakers are separates with 6x9s. if i want a tighter bass response, should i go 6.5s? whats the biggest mids i can fit in teh front doors without having to go to a shop for custom work? any help will be appreciated, thanks.

if you want to keep them 6x9 in the door i would go with either of these two ive used these several times with good results CL-69CX - CDT Audio 2-way 6 x 9 Component System         XS-69 - Image Dynamics 6x9 2 Way Component System hope this helps      in process of changing everything